The invention relates to infrared radiation detectors and, more particularly, to Lead-Salt infrared radiation detectors their methods of formation.
An infrared radiation detector responds to the thermal energy radiated by objects, such as animals, automobiles, and airplanes. This thermal energy is typically not visible to the human eye. Accordingly, by using an infrared radiation detector, objects that are not visible may be perceived and/or alternative views of visible objects may be obtained.
Infrared radiation detectors are typically composed of numerous detector elements, each of which detects a portion of a scene. The detector elements may be formed monolithically on an integrated circuit that processes the output from the detector elements or formed on their own substrate and then coupled to the integrated circuit. Monolithic architectures are advantageous because they require fewer processing steps and suffer fewer performance losses due to absorption. Hybrid architectures, on the other hand, are advantageous because detector materials that are incompatible with single crystal silicon may be utilized to form a focal plane array.
Currently, several high performance hybrid infrared radiation detectors exist. These detectors typically have detector elements made of Mercury-Cadmium-Telluride (HCT) or Indium Antimonide (InSb), which are expensive and difficult to process. Moreover, to function properly, these detectors require cryogenic cooling, which is expensive to design, complex to operate, and unreliable.
Additionally, there are two standard options for infrared radiation detectors that operate close to room temperature. In the eight to twelve micron band, microbolometer technologies are used. Unfortunately, these devices have a relatively long time constantxe2x80x94on the order of ten milliseconds. In the one to two micron band, Indium-Gallium-Arsenide (InGaAs) detector elements are used. Unfortunately, formation of these detectors requires complex Molecular Beam Epitaxy Deposition.
While other materials are known to exhibit acceptable photoconductive properties, creating hybrid detector elements may be difficult. For example, achieving an appropriate chemical reaction between the detector element material and the material on which the detector elements are to be formed may be difficult. Moreover, the surface on which the detector elements are to be formed may not have an appropriate geometry for the formation. Furthermore, achieving proper Ohmic contact between the detector elements and the integrated circuit may be difficult.
The present invention provides systems and methods that reduce and/or eliminate at least some of the disadvantages with the prior art. Accordingly, at least in certain embodiments, the present invention provides a hybridized, Lead-Salt infrared radiation detector that has good performance without requiring cryogenic cooling.
In certain embodiments, a hybridized Lead-Salt infrared radiation detector includes a focal plane array having a substrate and a sensitized, delineated Lead-Salt layer upon the substrate, the delineations forming a plurality of sections in a two-dimensional array. The detector also includes electrical contacts for each of the sections and a common grid between the sections. The detector further includes a layer of conductive barrier material on each electrical contact, a layer of passivating material on each section, and a layer of fusible conductive material on each layer of conductive barrier material.
In particular embodiments, a method for forming a hybridized Lead-Salt infrared radiation detector includes forming a focal plane array. Forming the focal plane array includes depositing a Lead-Salt layer upon a substrate, sensitizing the Lead-Salt layer, and delineating the Lead-Salt layer into a plurality of sections, the sections forming a two-dimensional array. Forming the focal plane array also includes forming electrical contacts for each of the sections and a common grid between the sections and depositing a layer of conductive barrier material on each electrical contact. Forming the focal plane array further includes depositing a layer of passivating material on each section and depositing a layer of fusible conductive material on each layer of conductive barrier material.
The present invention has several technical features. For example, the invention allows short wavelength infrared (SWIR) and medium wavelength infrared (MWIR) detectors to be readily manufactured. As another example, in certain embodiments, the detector elements can operate at or close to room temperature. Accordingly, the detectors can avoid the cost and complexity of cryogenic cooling. As a further example, in particular embodiments, the detector elements exhibit time constants on the order of one to ten microseconds, allowing a high frame rate, which may be useful for tracking applications where the scene varies rapidly. As still a further example, in some embodiments, the detector elements may have a relatively small pitch, such as, for example, less than approximately thirty microns. Having a smaller pitch allows for more densely populated detector elements on a given integrated circuit, which increases resolution, or for reducing the size of the integrated circuit for a given focal plane array format, which reduces the cost of the integrated circuit and the complexity of the optics. As another example, in certain embodiments, the processing of the Lead-Salt layer allows increased detectivity of the detector elements. Of course, some embodiments may contain one, some, or all of these technical features.
Other technical features will be readily apparent to those skilled in the art from the following figures, written description, and claims.